1. Field of the Invention
This invention relates to improving the performance of a hydrostatic drive, especially a hydrostatic drive for a vehicle, by means of a regeneration circuit.
2. Background Information
Hemostatic drives are popular in applications where it is desirable to have good speed control under varying loads. They are also popular in hazardous, dirty, and nasty environments, such as coal mines, quarries, food processing plants, and on construction sites. Much effort has been expended in trying to increase the efficiency and performance ranges of hydrostatic drives. Hydrostatic drives are typically called, in the trade, closed loop systems, and comprise a fixed or variable displacement pump supplied with fluid by means of a charge pump.
Existing ways of obtaining a broader range of speed and torque in a hydrostatic drive with a given pump, motors, and engine combination comprise:
a) using a mechanical transmission with a variety of gearing arrangements in conjunction with one or more hydraulic motors, and PA1 b) valving to switch the hydraulic motors from a parallel circuit to a series circuit, and back again, as required.
Regeneration circuits are common to the trade on industrial equipment such as hydraulic presses. Regeneration circuits using rotary dividers are in the public domain for industrial equipment such as hydraulic presses. A publication illustrating gerotor rotary flow dividers in regeneration circuits is the American Society of Agricultural Engineers Paper No. 911596 "Gerotor Rotary Flow Divider" by George Morgan, P. E., Sales Manager, White Hydraulics, Inc. presented at the 1991 International Winter Meeting sponsored by the American Society of Agricultural Engineers at the Hyatt Regency Chicago, Chicago, Ill., December, 1991 which is hereby incorporated by reference. The American Society of Agricultural Engineers is located at 2950 Niles Road, St. Joseph, Mich., 49085-9659, USA, Ph. (616) 429-0300, Fax: (616) 429-3852.
Hydra-Pneu Consulting, Inc., 726 Outer Gray Drive, Newburgh, Ind. 47630-1517, Ph. (812) 853-3234, conducted a course in "Advanced Fluid Power" in 1991, where the instructor, Bud Trinkel, discussed the use of a rotary flow divider in an open loop press circuit. One of his previous students had developed it, and brought it to his class. Applicant then introduced it to his employer at the time, White Hydraulics, Hopkinsville, Ky. The engineers doubted it would work. It did.
The state of the art uses flow dividers in regeneration circuits for open loop, fixed displacement circuits. Neither regeneration circuits, nor regeneration circuits with rotary flow dividers, nor regeneration circuits with gerotor rotary flow dividers have ever been used with closed loop hydrostatic drives, especially vehicle closed loop hydrostatic drives.
With existing state-of-the-art hydrostatic drives with bi-directional pumps, approaches to proper filtration and cooling are limited. High pressure filtration arrangements are expensive, so typically are not used on mobile equipment. Similarly, for coolers to withstand the high pressures of the hydrostatic closed loop system flows, the designs would be heavy and expensive. Consequently, choices for filtration and cooling, practically, are limited to case drain flow or inlet charge pump flow, or hot oil shuttle arrangements where a small amount of flow is cooled and filtered at a time. This means that the bulk of the flow is not properly filtered or cooled, and this results in componentry wear which reduces componentry life.
As will be seen from the subsequent description, the preferred embodiments of the present invention broadens the performance range of a closed loop hydrostatic drive in a novel manner and overcomes exisiting limitations of closed loop hydrostatic drives.